1. Field of the Invention
The present invention relates to an aluminum electrolytic capacitor device, which is employed in a switching power circuit, etc.
2. Description of the Related Art
A conventional aluminum electrolytic capacitor is small in size but large in capacitance since its capacitance per unit area is significantly large. To meet the demand for down-sized electronic circuit component parts, the size of the aluminum electrolytic capacitor is further reduced and the capacitance thereof is further increased. As shown in FIG. 1, the diameter of a cylindrical hole of the core portion of a capacitor device is normally 3 to 6 mm.
If such an aluminum electrolytic capacitor is subjected to abnormal stress, such as overvoltage, formation current locally flows into a portion where an anode foil and a cathode foil are not parallel. Such formation current causes an exothermic reaction, which, in turn, causes the electrolyte to evaporate. As a result gas pressure increases, generating a force to expand the capacitor device both outward and inward. Since the outside of the device is fastened by a tape, the electrode foils in an outer portion are not substantially affected. However, the electrode foils close to the core cylindrical hole are buckled toward the core hole by the increased pressure, causing a short circuit between the electrodes. In some cases, a spark caused by the short circuit ignites the electrolyte, and the capacitor device burns.